For aluminum alloy 6005A car body extrusion profile with complex section，the extrusion process was simulated by Hyperxtrude software, and the distributions of temperature field, velocity field and deformation field during the extrusion process were analyzed. Then, the aluminum alloy profile was extruded in the extruding machine of 75 MN, and the microstructures and mechanical properties of aluminum alloy profile were investigated by optical microscopy（OM）, scanning electron microscopy（SEM）and hardness test. Furthermore, the microstructures and properties of aluminum alloy profiles during extrusion process were studied, and the simulation results were compared. The results show that for the complex section dimension of extrusion profile, the distributions of temperature, velocity and deformation in the same section are quite different. Corresponding to the position with higher temperature, faster velocity and large deformation, the finer grain with more second phase and higher hardness were obtained. Due to the significant thermal effect during the extrusion process, the temperature of profile tail is higher than that of the profile head, resulting in a more uniform microstructure, more dispersing second phase and higher hardness of aluminum alloy profile tail.